Separation of alkoxyacetones and alkoxy-2-propanols from mixtures thereof



2,805,983 oxY-z-PROPANOLS Sept- 10, 1957 L. H. HoRsLEY SEPARATION oF ALKOXYACETONES AND ALK FROM MIXTURES THEREOF Filed April 5, 1954 INVENTOR l. ee- H. Hors/ey BY M i( 7 ATTORNEYS.

United States atent O SEPARA'IIN OF ALKOXYACETONES AND ALKOXY-Z-PRGPANGLS FROM MIXTURES THEREOF Application April 5, 1954, Serial No. 420,837

16 Ciaims. (Cl. 202-42) This invention pertains to a method for separation of alkoxyacetones and/ or alkoxy-2-propanols from mixtures thereof which ordinarily form azeotropes during distillation.

In the preparation of` alkoxyacetones from the corresponding alkoxy-Z-propanols, e. g. by dehydrogenation or oxidation of the alkoxy-Z-propanol, there is usually obtained a reaction product mixture comprising both the alkoxyacetone product and the unreacted alkoxy-Z-propanol starting material. The separation of such a reaction product by distillation is usually dicult, if not impossible, due to the formation of an azeotropc mixture of the alkoxyacetone and the corresponding alkoxy-Z-propanol during distillation.

It has been proposed to separate such mixtures by esterifying the allroxy-Z-propanolV component with a suitable acid, separatingr the resulting ester from the alkoxyacetone, e. g. by fractional distillation, and thereafter saponifying the separated ester to regenerate the alkoxy-2-propanol. It has also been proposed to make chemical derivatives of the alkoxyacetone, such as the bisulte addition product, to separate such derivatives from the alkoxy-Z-propanol component of the mixture, and subsequently to regenerate the alkoxyacetone from its purified derivative.

From a practical standpoint, these proposals have been unsatisfactory for one or more of several reasons. The procedures require additional chemical process steps and the expenditure of additional raw materials. The degree of purification is often not satisfactory and the recovery of the desired product is sometimes poor. Usually only one component of the mixture can be satisfactorily recovered in pure form. For these reasons, the known methods of separating such mixtures are not well adapted to commercial use.

U. S. Patent 2,324,255 describes a method for separation of azeotropic mixtures of alcohols and ketones by redistillation at a different pressure, whereby the composition of the azeotrope changes to permit obtaining at least one of the components in a form substantially free of the other. Its method is not satisfactorily eective for the separation of alkoxyacetones from alkoxy-Z-propanols, presumably because the presence of the alkoxy group sufticiently modies these materials that they no longer behave as simple ketones and alcohols.

An object of this invention is to provide an improved method for separation of alkoxyacetones and/ or allroxy-Z- propanols from mixtures thereof which ordinarily form y azeotropes during distillation.

A further object is to provide such a method whereby at least one member of the group consisting of alkoxyacetones and alkoxy2-propano1s can be separated from azeotropic mixtures thereof in a form substantially free from theother.

A further'object is to provide such a methodwhich is commercially practical.

Other objects and advantages following description.

will be evident from the The objects of this invention are attained in a new and 2,8i5,983 Patented Sept. 10, 1957 rice improved method, more completely described hereinafter, in which method mixtures of alkoxyacetones and alkoxy- Z-propanols, which ordinarily form azeotropes with one another during distillation, are fractionally distilled in the presence of a co-distillation agent which forms lowerboiling azeotropes with the alkoxyacetones, whereby the lower-boiling azeotropes of the alkoxyacetones and the co-distillation agent are separatedfrom residues which are enriched in respect to the alkoxy-Z-propanols. The alkoxyacetone and the co-distllation agent contained in the lower-boilingy azeotropic distillate can be separated from each other by redistillation of that distillate at a distillation pressure which is substantially different, i. e. either higher or lower, than the pressure at which the distillate was first obtained. At such different pressure, a second distillate and a second residue are obtained, the compositions of which are different from each other and from that of the iirst distillate. Depending on the pressure conditions employed in the second distillation, either the residue or the distillate therefrom consists of, or is rich in, the alkoxyacetone. Instead of redistilling the rst distillate, other means, e. g. chemical means, can be employed to effect a separation thereof. Y

The drawing is a iiow sheet of a continuous mode of practicing the invention and is self-explanatory.

The invention is applicable to the separation of azeotropic mixtures of alkoxyacetones, i. e. l-alkoxy-Z-propanones, and the corresponding l-alkoxy-Z-propanols, particularly mixtures of lower alkoxyacetones and lower alkoxy-2-propanols such as those having from four to six carbon atoms in the molecule (that is, having from one to three carbon atoms inthe alkoxy group), e. g. mixtures of methoxyacetone and l-methoxy-Z-propanol; ethoxyacetone and l-ethoxy-Z-propanol; propoxyacetone and lpropoxy-Z-propanol; isopropoxyacetone and l-isopropoxy- 2-propan0l.

The added agent employed herein to provide an azeotrope separable from the alkoxy-Z-propanol by distillation is an unsubstituted monohydric aliphatic alcohol, preferably such an aliphatic alcohol having a normal boiling point of from about 78 to about 160 C., i. e. the unsubstituted monohydric aliphatic alcohols having from 2 to 6 carbon atoms in the molecule, including the saturated and unsaturated aliphatic alcohols such as ethanol, the propanols, allyl alcohol, the butanols, methallyl alcohol, the pentanols, and the hexanols. Herein the term faliphatic alcohol refers to such an unsubstituted monohydric aliphatic alcohol. Preferably, the aliphatic alcohol is chosen to have a boiling point close to the boiling point of the alkoxy mixture under the conditions of the distillation, so that the azeotropic distillate obtained contains an appreciable proportion of bothvthe alkoxyacetone and the aliphatic alcohol. In other words, the higher boiling aliphatic alcohols are preferably employed with the higher boiling, higher molecular weight alkoxy mixtures. These aliphatic alcohols form azeotropic mixtures with the alkoxyacetones, but do not form azeotropic mixtures with alkoxy-2-propanols. Therefore, the azeotropic mixtures of aliphatic alcohols with alkoxyacetones can be separated by distillation from alkoxy-Z-propanols. Thereafter, the alkoxyacetones can be separated from the azeotropic mixtures thereof with the aliphatic alcohols.byredistillation at a different pressure, as hereinafter described.

Either or both of the distillation steps of Athis invention may be carried out continuously or in a batchwise manner and either may be operated independently of the other. Preferably, in commercial practice, the distillation steps are operated continuously and in an integrated fashion. Such preferred operation will be described herein, recognizing that the preferred operation can be modified in obvious ways.

In practice of the invention, one of thevaforementioned paratus is required, althoughLobviously, the more eiicient the fractionating column and the Vmore rened the operation,V the more effective will be the separationV obtained. The distillation may be Acarried out at, above, or below, atmospheric pressure, but is preferably carried out at such a pressure that the distillate contains appreciable proportions of both the alkoxyacetone and the added aliphatic alcohol contained in` the distillation charge. For a'given kind of distillation charge, the lower the distillation pressure, the .richer theY azeotrope distillate is in the alkoxyacetonecomponent and the less aliphatic alcohol is `required to eect the-desired separation.

The proportion ofaliphatic alcohol which isadded tothe alkoxyacetone and alkoxy-2ypropanol mixture is dependent uponV the kind of aliphatic alcohol used, the kind and proportion of alkoxyacetone and alkoxy-Z-prof panol in the mixture and Vupon the pressure under which the first step of distillation is operated.

Therdistillate, obtained by fractional distillation of the mixture of l-alkoxyQ-.propanona- 1-alkoxy-2-propanol and the added aliphatic alcohol, comprises the l-.alkoXy-Z- propanone and the added aliphatic alcohol and is substantially free of the Vl-alkoxy-2-propanol. The residue so obtained is enriched in respect to the l-alkoxy-Z-propanol. If the fractional distillation is carried far enough, the residue can be substantially free of l-alkoxy-2-p'ropanone. For example, by fractional distillation of 50 mm. of mercury absolute pressure of a mixture of methoxyacetone, lmethoxv2propanol and l-propanol, there was obtained a distillate consisting of 40 percent by Weight methoxyacetone and 60'percent by weight l-propanol, and a residue consisting substantially of 1-methoxy- Z-propanol.

In the second step ofthe method, the azeotropic mixture of alkoxyacetone and aliphatic alcohol, obtained as described above, can be redistilled at a different distillation pressure. Therebythere is obtained a distillate, which is either richer or poorer than thedistillation feed in the aliphatic alcohol component Vand poorer or richer in the alkoxyacetone component, depending upon whether this second distillation is carried out ata higher or a lower pressure than that ofthe rst distillation. In other words, when the secondy distillation is carried out'at a higher pressure than the first, the proportion of aliphatic alcohol is greater, and the proportion of alkoxyacetone is less, in the second Ydistillate than inthe rst distillate. Under such conditions, the residueY can be made to( consist substantially of, thealkoxyacetone. The higher the pressure at which this Vsecond step distillation is operated, the less Valltoxyarcetone there is in the second distillate. Il"V this second distillation pressure is high enough, the distillation may become non-azeotropic and the distillate then be substantially the aliphatic alcohol. Obviously, the distillation pressure must be below the critical pressure and the distillation temperature must be below the decomposition temperaturerof any component of the system. By Way of example, the azeotrope described above, obtained by distillation at 50mm. of mercury absolute pressure and consisting `of 40 percent methoxyacetone and 60 weight percent l-propanol, was redistilled at atmospheric pressure, whereby there was is enriched in, and

the second distillation pressure, the larger is the proportion of alkoxyacetone in the second distillate. If this second distillation pressure is low enough, the distillation may become non-azeotropic and the second distillate then be substantially the alkoxyacetone.

That fraction from the second step distillation which consists of, or is rich in, aliphatic alcohol can be returned to the feed to the rst step distillation, thereby recovering the minor proportion of alkoxyacetone contained in such fraction and also thereby supplying the codistillation agent necessary in the feed to the first step distillation.

The method of the invention can be practiced in continuous manner by carrying out the two distillation continuously and simultaneously as shown by the ilow sheet in the drawing. To the first distillation is fed a mixture of alkoxyacetone and alkoxy-2propanol together with one of the aforementioned aliphatic alcohols as a coobtained a distillate consisting of l5 weight percent methoxyacetone and 85 weight percent l-propanol and a residue consisting essentially of methoxyacetone.

Alternatively, the first distillate can beredistilled at a pressure substantially lower than that of the rst distillation, thereby obtaining a second distillate which is richer ,in the alkoxyacetone and poorer in the aliphatic alcohol than the first distillate. Under such conditions, the residue from the second distillaton is enriched in, and can ccnsist substantially of, the aliphatic alcohol.. The lower distillation agent. Continuously from the :Erst distillation step is removed a residue which consists of, or is rich in, the alkoxy-Z-propanol'and a distillate which cdmprises an azeotropic mixture of the alkoxyacetone and the aliphatic alcohol and which is substantially free of the 'alkoxy-Z-propanol. That distillate from the first Step distillation is then Yfed to a second distillationV step, at a distillation pressure different 'from that of the rst distillation step. Continuously from the second distillation step is removed a residue fraction and a distillate fraction, in one of which the proportion of aliphatic alcohol is greater than in the feed to that second distillation step. The other fraction consists of, or is rich in, the alkoxyacetone, and is substantially free of alkoxy-Z-propanol. That fraction from the second distillation step which consists of, or is rich in, the aliphatic alcohol co-distillation agent is returned to the first distillation step together` with the alkoxyacetone and alkoXy-Z-propanol starting material. Thereafter, only make-up quantities of aliphatic alcohol are required to be added to the process, since thel aliphatic alcohol is effectively cycled through the two distillation steps.

The following examples illustrate the invention, but are not to be construed as limiting its scope.

l Example l was redistilled at atmospheric pressure, whereby thereY was obtained a seconddistillate consisting of 15 percent by weight meth-oxyacetone and percent by weight n-propyl alcoholtandra ksecond residue Which' was sub- Y stantially pure rnethoxyacetone. 4

Example 2 Y 1-ethoxy-2-propano1was oxidativelydehydrogenated by percent by weight Yisopropyl"al- Y heating to 100`C., drawing air therethrough and passing the gases, i. e. air laden with vapors of 1-ethoxy2- propanol, over a silver gauze catalyst at a temperature of 415-440 C. at atmospheric pressure. From the resulting reaction product there was obtained a mixture containing 86 percent by weight ethoxyacetone and 14 percent by weight 1-ethoxy-2-propanol, which mixture distilled azeotropically at atmospheric pressure and could not be separated by simple distillation. To 240 grams of that mixture was added 200 grams of n-butyl alcohol (l-butanol). The resulting mixture was distilled at 18 mm. of mercury absolute pressure. There were obtained 310 grams of a distillate fraction containing 62 percent by weight ethoxyacetone and 38 percent by weight n-butyl alcohol and a l-ethoxy-Z-propanol residue containing only 3.5 percent by weight ethoxyacetone (corresponding to 96.5 percent by weight l-ethoxy-2-propanol). The 1- ethoxy-Z-propanol residue was suitable for returning to the oxidation step. The S-gram distillate fraction was redistilled at atmospheric pressure, whereby there were obtained a distillate containing 22 percent by weight ethoxyacetone and 78 percent by weight n-butyl alcohol, and a residue which analyzed 91 percent by weight ethoxyacetone.

I claim:

1. A method which comprises subjecting to fractional distillation a mixture of a 1-alkoxy-2-propanone and the corresponding 1-alkoxy-2-propano1 that forms an azeotrope when distilled at approximately atmospheric pressure, the alk'oxy group in the l-alkoxy-Z-propanone and 1-alkoxy-2-propanol having from one to three carbon atoms, together with an unsubstituted monohydric aliphatic alcohol having a normal boiling point between 78 and 160 C. and within 30 C. of the boiling point of the 1-alkoxy-2-propanone, to obtain a mixture of the aliphatic alcohol and the 1-alkoxy-2-propanone as distillate and to obtain a residue which is richer than the starting material in the l-alkoxy-Z-propanol.

2. A method laccording to claim 1 wherein the l-alkoxy-2-propanone and the 1-alkoxy-2-propanol are l-methoxy-2-propanone and l-methoxy-Z-propanol, respectively.

3. A method according to claim 1 wherein the l-alkoxy-2-propanone and the 1-alkoxy-2-propanol are l-ethoxy-2-propanone and 1ethoxy2propanol, respectively.

4. A method according to claim 1 which comprises the further step of redistilling the distillate at a distillation pressure which is substantially dilerent from that at which the distillate was obtained to form a second distillate and a second residue, one of which lis richer in the 1-alkoxy-2-propanone than is the other.

5. A method -according to claim 1 which comprises the further step of redistilling the distillate at a distillation pressure which is substantially higher than that at which the distillate was obtained to form a second distillate and a second residue, which second residue is richer than the second distillate in 1-alkoxy-2-propanone.

6. A method for the separation of a 1-alkoxy-2-propanol from a mixture thereof with the corresponding 1- alkoxy-Z-propanone that is azeotropic when distilled at approximately atmospheric pressure, the alkoxy group in the l-alkoxy-Z-propanone and l-alkoxy-2-propanol having from one to three carbon atoms, which method comprises distilling the mixture together with an unsubstituted monohydric aliphatic alcohol having a normal boiling point between 78 and 160 C. and within 30 C. of the boiling point of the 1-alkoxy-2-propanone 4to obtain a mixture of the aliphatic alcohol and the 1-alkoxy-2-propanone as distillate and to obtain a residue which consists substantially of l-alkoxy-Z-propanol.

7. A method according to claim 6 wherein the 1-alkoxy-2-propanol and 1-alkoxy-2-propanone are l-methoxy- 2-propanol and 1-methoxy-2-propanone, respectively.

8. A method according to claim 6 wherein the 1-alkoxy-2-propanol and 1-alkoxy-2-propanone-are l-ethoxy- 2-propanol and lethoxy-Z-propanone, respectively.

9. A method for the separation of a 1-alkoxy-2-propanone from a mixture thereof with the corresponding 1- alkoxy-Z-propanol that is azeotropic when distilled at approximately Vatmospheric pressure, the alkoxy group in the l-alkoxy-Z-propanone and l-alkoxy-Z-propanol having from one to three carbon atoms, which method comprises distilling the mixture together with an unsubstituted monohydric aliphatic alcohol having a normal boiling point between 78 and 160 C. and within 30 C. of the boiling point of the l-alkoxy-Z-propanone at a first distillation pressure to obtain a distillate which contains an appreciable proportion of the l-alkoxy-Z-propanone and is substantially free of l-alkoxy-Z-propanol, and redistilling said distillate at a second distillation pressure which is substantially higher than the first distillation pressure to obtain a second distillate which is richer than the iirst distillate in the aliphatic alcohol and to obtain a second residue which consists substantially of 1-alkoxy-2-propanone.

10. A method according to claim 9 wherein the l-alkoxy-Z-propanone and 1-alkoxy-2-propanol are 1-methoxy- 2-propa11one and 1-methoxy-2-propanol, respectively.

11. A method according to claim 9 wherein the 1-alkoxy-2-propanone and l-alkoxy-Z-propanol are l-ethoxy- 2-propanone and 1-ethoxy-2-propanol, respectively.

12. A method for the separation of a mixture of 1-alkoxy-Z-propanol and the corresponding 1-alkoxy-2-propanone, each having from one to three carbon atoms in its alkoxy radical, which mixture is azeotropic when distilled at approximately atmospheric pressure, comprising the steps of continuously feeding said mixture to a rst fractional distillation together with an unsubstituted monohydric aliphatic alcohol having a normal boiling point between 78 and 160 C. and within 30 C. of the boiling point of the 1-alkoxy-2-propanone, continuously removing a rst distillate fraction and a first residue fraction, which irst distillate fraction contains appreciable proportions of the l-alkoxy-Z-propanone and of the aliphatic alcohol and is substantially free of the l-alkoxy-'Z-propanol, and which first residue fraction consists substantially of the 1-alkoxy-2-propanol, continuously feeding said rst distillate fraction to a second fractional distillation at a distillation pressure which is substantially different from the distillation pressure in the first fractional distillation, continuously removing a second distillate fraction and a second residue fraction, one of which second fractions is richer than the irst distillate fraction in the l-alkoxy-Z-propanone and the other -of which second fractions is richer than the first distillate fraction in the aliphatic alcohol, and continuously returning to the first fractional distillation that second fraction which is richer in the aliphatic alcohol.

13. A method according to claim 12 wherein the second fractional distillation is carried out at a distillation pressure which is substantially higher than the rst distillation pressure to obtain continuously a second distillate fraction which is appreciably richer than the first distillate fraction in the aliphatic alcohol and a second residue which consists substantially of 1-alkoxy2propa none, and continuously returning the second distillate fraction to the first fractional distillation.

14. A method according to claim 13 wherein the l-alkloxy-2-propanol and 1-alkoxy-2-propanone are l-methoxy- Z-propanol fand l-methoxy-Z-propanone, respectively.

15. A method according to claim 13 wherein the l-alkoxy-2-propanol and l-alkoXy-Z-propanone are l-ethoxy- 2-propanol and l-ethoxy-Z-propanone, respectively.

16. In a method for making a 1-alkoxy-2-propanone by dehydrogenation of a corresponding 1-alkoxy-2-propano1 that has from 1 to 3 carbon atoms in its alkoxy radical whereby there is obtained a mixture of the 1-alkoxy-Z-propanol and the l-alkoxy-Z-propanone that forms an azeotrope when distilled at approximately atmospheric 7 pressure, the steps'of separating the 1alkoxy2propanol References Cited in. the'le of this patent Y from the ldalkoXy-Z-propanone by subjecting that mix- UNITED STATES PATENTS ture to fractional. distillation together with. an unsubstiing that residue to the dehydrogenation step. 

1. A METHOD WHICH COMPRISES SUBJECTING TO FRACTIONAL DISTILLATION A MIXTURE OF A 1-ALKOXY-2-PROPANONE AND THE CORRESPONDING 1-ALKOXY-2-PROPANOL THAT FORMS AN AZEOTROPE WHEN DISTILLED AT APPROXIMATELY ATMOSPHERIC PRESSURE, THE ALKOXY GROUP IN THE 1-ALKOXY-2-PROPANONE AND 1-ALKOXY-2-PROPANOL HAVING FROM ONE TO THREE CARBON ATOMS, TOGETHER WITH AN UNSUBSTITUTED MONOHYDRIC ALIPHATIC ALCOHOL HAVING A NORMAL BOILING POINT BETWEEN 78* AND 160*C. AND WITHIN 30*C. OF THE BOILING POINT OF THE 1-ALKOXY-2-PROPANONE, TO OBTAIN A MIXTURE OF THE ALIPHATIC ALCOHOL AND THE 1-ALKOXY-2-PROPANONE AS DISTILLATE AND TO OBTAIN A RESIDUE WHICH IS RICHER THAN THE STARTING MATERIAL IN THE 1-ALKOXY-2-PROPANOL. 